Disperse dyes which are convertible into a thermo-migration fast form

A disperse dye of the formula ##STR184## where E is D--N.dbd.N-- or ##STR185## where D is a carbocyclic or heterocyclic diazo component other than aminobenzisothiazole,

• X is hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, halogen, C.sub.1 -C.sub.4 alkylsulfonylamino, a group of the formula --NH--U--R.sup.3 where U is --CO-- or --SO.sub.2 -- and R.sup.3 is C.sub.1 -C.sub.4 -alkyl which is unsubstituted or substituted by hydroxy, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkoxycarbonyl, halogen or phenyl or R.sup.3 is phenyl which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, halogen, nitro or C.sub.1 -C.sub.4 -alkylcarbonylamino or
• X is a group of the formula --NH--CO--NHQ where Q is hydrogen, C.sub.1 -C.sub.4 alkyl or phenyl,
• Y is hydrogen, halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkoxy-C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 alkoxy-C.sub.2 -C.sub.4 alkoxy,
• R.sup.1 is C.sub.1 -C.sub.12 alkyl, C.sub.2 -C.sub.6 alkenyl or phenyl, or Y and R.sup.1, together with the nitrogen atom and the two C atoms joining them, form a 6-membered ring which is unsubstituted or substituted by 1 to 4 methyl groups,
• B is a straight-chain or branched C.sub.2 -C.sub.6 alkylene,
• Z is O or S and
• V.sup.1 is a group which eliminates a radical HV.sup.1 at temperatures between 180.degree. and 240.degree. C. selected from the group consisting of ##STR186## which are unsubstituted or substituted in the phenyl ring by C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkoxycarbonyl or halogen, where
• R.sup.2 is C.sub.1 -C.sub.6 alkyl and
• R.sup.6 is C.sub.1 -C.sub.6 alkyl or C.sub.3 -C.sub.7 cycloalkyl.